But he also made plenty of time for partying in Sin City—sans Jessica...

On Wednesday night, Justin had dinner at Nobu at the Hard Rock Hotel and Casino with a group of guys. After they hit the gambling tables, they continued the party at Wasted Space.

Later in the night, J.T. headed to LAX, where Kobe Bryant and Lamar Odom were hosting a bash. He even shared a table with former 'N Sync bandmate Chris Kirkpatrick.

"Justin seemed to be having a good time hanging out with old friends," a witness says.

But while mom continues to stick to the Team Justin line that everything is copacetic with his love life, we're hearing that in private, he's telling pals he's bid "bye bye bye" to Jessica, who stayed back in Los Angeles for the weekend.

Yes, a source close to Justin tells us the couple has indeed called it quits.

The insider also says there's no truth to the romance rumors between Justin and Rihanna.

For now, at least, we'll give Mama Timberlake the benefit of the doubt...